The researchers set up arrays of petri dishes stuck to a board next to the dryers to measure the splatter. According to Microbe Post:

Measuring splatter at different heights right next to the device, jet air dryers produced (on average) 1,300 times more plaques than paper towels, and 60 times more than warm air dryers. The authors note that the maximum number of plaques were found between 0.75 and 1.25 metres – about the height of a small child’s face when standing next to a parent. Jet air dryers also aerosolised the virus much more effectively than the other two methods, with particles remaining in the air for at least 15 minutes after drying. These may eventually settle and contaminate other surfaces.

Our research and results over the years have revealed time and again that single-use towels are the safest way to dry one’s hands in the washroom. This virus study delivers further proof that when it comes to hygiene, drying one’s hands with a single-use paper towel is the safest way to reduce the spread of viruses after a visit to the washroom.

The towel makers even provide this handy infographic to make their point:

TreeHugger is very interested in this because for years we have been stressing that air dryers have far lower carbon and water footprints than paper towels. In a life cycle analysis comparing the two, going right back to the manufacture of the dryer, the difference was yuuuge:

…a drier, over its life time, will result in a global warming burden of 1.6 tonnes of CO2. This is an equivalent burden to that associated with a car travelling 5 100 km. Over the same period, the use of paper towels would result in an average CO2 burden of 4.6 tonnes. This is an equivalent burden to that associated with a car travelling 14 500 km.

And that LCA was done a decade ago, when dryers were less efficient and electric power sources burned more coal and put out much more CO2. In fact, it was done before the Dyson Airblade existed, and it uses 83 percent less energy.

Dyson has been dealing with this kind of criticism for years; there were earlier studies where Dyson complained about the methodology, and they are complaining about this one in the Independent:

Peter Henderson, a spokesman for Dyson, said that in everyday situations, it would be unlikely for hands to have such high levels of virus contamination as used in the study and that, in any case, the process of washing hands before they are dried has, as its very purpose, the aim of getting rid of germs. “The paper towel industry has scaremongered with this [type of] research for the past four years. It has been conducted under artificial conditions, using unrealistically high levels of virus contamination on unwashed, gloved hands.”

Canada Ministry of Health/Public Domain

Really, they have a point. Besides, the real problem is the fact that people are not washing their hands or doing a lousy job in the first place. Properly wash your hands with soap (counting to twenty or singing Happy Birthday to You) and there won't be a whole lot of bacteria to spread. A modern bath with touchless taps and dryers is going to be a lot more sanitary than touching towel dispensers and taps. It has a much lower carbon footprint too.